Remember to update the write barrier when storing into...

src/x64/macro-assembler-x64.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 173 matching lines @@
   ASSERT(!object.is(rsi) && !value.is(rsi) && !smi_index.is(rsi));
 
   // First, check if a remembered set write is even needed. The tests below
   // catch stores of Smis and stores into young gen (which does not have space
   // for the remembered set bits.
   Label done;
   JumpIfSmi(value, &done);
 
   RecordWriteNonSmi(object, offset, value, smi_index);
   bind(&done);
+
+  // Clobber all input registers when running with the debug-code flag
+  // turned on to provoke errors. This clobbering repeats the
+  // clobbering done inside RecordWriteNonSmi but it's necessary to
+  // avoid having the fast case for smis leave the registers
+  // unchanged.
+  if (FLAG_debug_code) {
+    movq(object, bit_cast<int64_t>(kZapValue), RelocInfo::NONE);
+    movq(value, bit_cast<int64_t>(kZapValue), RelocInfo::NONE);
+    movq(smi_index, bit_cast<int64_t>(kZapValue), RelocInfo::NONE);
+  }
 }
 
 
 void MacroAssembler::RecordWriteNonSmi(Register object,
                                        int offset,
                                        Register scratch,
                                        Register smi_index) {
   Label done;
+
+  if (FLAG_debug_code) {
+    Label okay;
+    JumpIfNotSmi(object, &okay);
+    Abort("MacroAssembler::RecordWriteNonSmi cannot deal with smis");
+    bind(&okay);
+  }
+
   // Test that the object address is not in the new space.  We cannot
   // set remembered set bits in the new space.
   movq(scratch, object);
   ASSERT(is_int32(static_cast<int64_t>(Heap::NewSpaceMask())));
   and_(scratch, Immediate(static_cast<int32_t>(Heap::NewSpaceMask())));
   movq(kScratchRegister, ExternalReference::new_space_start());
   cmpq(scratch, kScratchRegister);
   j(equal, &done);
 
   if ((offset > 0) && (offset < Page::kMaxHeapObjectSize)) {
@@ skipping 29 matching lines @@
     // record write code isn't going to save us any memory.
     if (generating_stub()) {
       RecordWriteHelper(this, object, dst, scratch);
     } else {
       RecordWriteStub stub(object, dst, scratch);
       CallStub(&stub);
     }
   }
 
   bind(&done);
+
+  // Clobber all input registers when running with the debug-code flag
+  // turned on to provoke errors.
+  if (FLAG_debug_code) {
+    movq(object, bit_cast<int64_t>(kZapValue), RelocInfo::NONE);
+    movq(scratch, bit_cast<int64_t>(kZapValue), RelocInfo::NONE);
+    movq(smi_index, bit_cast<int64_t>(kZapValue), RelocInfo::NONE);
+  }
 }
 
 
 void MacroAssembler::Assert(Condition cc, const char* msg) {
   if (FLAG_debug_code) Check(cc, msg);
 }
 
 
 void MacroAssembler::Check(Condition cc, const char* msg) {
   Label L;
@@ skipping 2279 matching lines @@
 CodePatcher::~CodePatcher() {
   // Indicate that code has changed.
   CPU::FlushICache(address_, size_);
 
   // Check that the code was patched as expected.
   ASSERT(masm_.pc_ == address_ + size_);
   ASSERT(masm_.reloc_info_writer.pos() == address_ + size_ + Assembler::kGap);
 }
 
 } }  // namespace v8::internal